Repair of dislocated bone involves two primary steps: realignment of the dislocated fragments or segments and stabilization of the bone. Dressings such as plaster or oil-soaked linen and wire have been used since antiquity for bone stabilization, but wire emerged as the prevalent appliance for bone stabilization in the nineteenth century.
Placement of wire loops through holes drilled in bone has long been an accepted technique, but more recent experience, during and after World War II, suggested that bone repaired with wire loops is not rigidly stable. The advent of mechanization and concomitant faster travel resulted in high velocity injuries more severe in nature than those previously encountered. Experience in treatment of such injuries has made it evident that bone fragments connected by wire loops are free to hinge along the fracture line. This bone fragment mobility interferes with healing and results in delayed recovery, skeletal deformity including midfacial shortening, and high rates of infection. Patients with complex injuries have often been crippled or disfigured for life, and many such injuries have been fatal.
Crude metal plates were introduced in Europe in approximately 1957 for the repair of orthopedic fractures. These plates, which were secured to bone with screws, advantageously prevented the bone fragment mobility that is often associated with wire-stabilized injuries. Subsequent generations of plates and fasteners, together with new instruments, allowed rigid stabilization of orthopedic and craniofacial fractures to become a reality. Complex, comminuted and severely dislocated fractures could then be effectively treated.
Typical of plates presently provided for cranial and facial osteosynthesis include those of the Wurzburg, Steinhauser and Champy systems sold in the United States by Walter Lorenz Surgical Instruments, Inc., Jacksonville, Florida, plates of Synthes, Inc., Basel, Switzerland and Paoli, Pennsylvania, and compression plates provided by Howmedica International, Inc., Kiel, Federal Republic of Germany. These plates present common, severe disadvantages, however.
Such plates typically comprise small, generally flat, elongated sections of metal. The sections contain round and perhaps elongated screw holes at various points along their lengths for fastening the sections to bone. The sections may be linear, curved, T-shaped, L-shaped or otherwise angled in their generally planar dimensions for positioning on various portions of the skeleton.
Because no surface of the human skeleton is flat, existing plates must be extensively twisted, formed and bent during surgery to conform to portions of the skeleton on which they are to be affixed. During a six to eight hour surgical procedure, as much as 30 to 45 minutes of time may be expended shaping and re-shaping metal plates. This additional time increases anesthesia requirements and operating room time and increases the potential of infection.
The inevitable over-bending and under-bending of plates during efforts to form the plates during surgery creates crimps and other surface imperfections in the plates and it alters their structural integrity due to metal fatigue. Surface imperfections can also irritate overlying tissue. Weakened structure due to excessive bending and twisting in the operating room is of paramount importance because it can lead to structural failure later; these plates frequently must remain in patients' faces for the rest of their lives and must undergo tremendous stresses, as for instance in the mandibular or ramus areas.
The heads of screws provided with present plates extend beyond the plane of the outer surfaces of the plates and create voids between bone and the periosteal lining. The contour of screw heads and often the plates are frequently transmitted through overlying soft tissue and thereby made visible on the patient's face; both screw heads and plates therefore frequently may be palpated beneath the skin's surface.
The planar nature of conventional plates increases this problem of transmission through the facial soft tissue. Rather than having edges which conform to and grip the bone, the edges of present plates frequently form a tangent with respect to the skeleton so that the patient may actually be able to push subcutaneous tissue between the plate edge and bone with his or her fingernail.
Known packaging techniques present additional difficulties. Plates and screws are presently provided on pegs or in slots together with installation tools in perforated metal boxes. They are arranged in various sizes, shapes and lengths and cannot be easily identified by name, so the surgeon finds it difficult to tell the nurse which plate will be used next. The plates and screws packaged in these metal boxes also require sterilization in an autoclave or other apparatus, so that addition valuable time prior to or during surgery is lost.
Conventional plates, screws and instruments are held in place by gravity in their metal boxes. If such a box is inverted while closed, the plates, screws and instruments become scrambled in the box. If the box is open while it is inverted or dropped, the plates, screws and instruments are scattered about the operational setting.
Screws must be delivered from the scrub nurse's station or table to the surgeon by means which allow them to be quickly and easily used. Present techniques include Phillips or cruciform head screwdrivers with clutches that grab the screwhead. The clutch sleeve is retracted once the screw is started into the bone. Such clutches are difficult to engage and disengage from screwheads, particularly after repeated use, because of rust in the clutch mechanism. The additional force required to disengage the clutch may jar delicate bone such as, for example, the bone of the inferior orbital rim. On the other hand, Phillips, slotted or cruciform screwdrivers without a clutch can disengage from the screwhead and interrupt insertion of the screw, alter the torque axis or alter screw penetration direction if the screw is self-tapping. Many existing screw designs also result in inadvertent disengagement or slippage of the screwdriver from the head. Existing slotted, cruciform or hexagonal-type screwheads all allow this disengagement.